The present invention relates to an optical pick-up device and an optical information recording reproducing apparatus.
Recently, DVD (Digital Versatile Disk) which is rapidly spreading as an optical recording medium of the image information or the like, can record the information of 4.7 GB per one surface when the red semiconductor laser of wavelength 650 nm and an objective optical system of a numerical aperture (NA) 0.65 are used. However, for the purpose that the information of higher density is recorded/reproduced at a high transfer rate, a requirement of further high densification and a much increase of capacity becomes strong. As universally well-known, for the purpose to attain the high densification and much increase of capacity of optical disk, it is sufficient when a diameter of a spot light-converged in the objective optical system is reduced, and for that, a reduction of wavelength of the laser light source or a high increase of numerical aperture of the objective optical system, is necessary.
Relating to the reduction of wavelength of the laser light source, a blue violet-semiconductor laser of wavelength 405 nm, or a blue violet SHG laser is putting in practical use, and by a combination of these blue violet laser light sources and the objective optical system of NA 0.65, for an optical disk of 12 cm diameter, the information of about 15 GB can be recorded per one surface. (hereinafter, in the present specification, an optical disk using the blue violet laser light source is named generally as “high density optical disk”).
Further, as for the much increase of NA of the objective optical system, a standard of optical disk by-which the light flux from the blue violet laser light source is light-converged by the objective optical system of NA 0.85 and the recording/reproducing of the information is conducted, is proposed, and in the optical disk of this standard, the information of about 23 GB per one surface can be recorded for the optical disk of 12 cm diameter.
Hereupon, in the high density optical disk using the objective optical system of NA 0.85, because the coma generated due to a skew of the optical disk is increased, the protective layer is designed thinner than in a case of DVD (thickness of the disk is 0.1 mm, while thickness of DVD is 0.6 mm), and the coma amount to the skew is decreased.
However, only by saying that the information can be adequately recorded/reproduced for such a high density optical disk, it can not be said that the value as a product of the optical disk player is sufficient. In the present time, when it is based on the actuality that for example, DVD or CD (Compact Disc) in which various information is recorded, is put in the market, it is not sufficient only in a case where the recording/reproducing of the information can be conducted on the high density optical disk. For example, a fact that the recording/reproducing of the information can be conducted adequately in the same manner also on the DVD or CD which are owned by the user, leads to an increase of the value of goods as the optical disk player for the high density optical disk. From such a background, it is required for an optical pick-up device mounted in the optical disk player for the high density optical disk that, while it keeps a compatibility also for any one of the high density optical disk, DVD, and CD, it has a performance by which the recording/reproducing of the information can be adequately conducted.
As a method by which, while it has a compatibility also for any one of the high density optical disk, DVD, and CD, the recording/reproducing of the information can be adequately conducted, a method by which optical parts for the high density optical disk, and optical parts for DVD or CD, are selectively switched corresponding to the recording density of the optical disk for which the information is recorded/reproduced, can be considered. However, because a plurality of optical parts are necessary, it is disadvantageous for the size reduction, and further, cost is increased.
Accordingly, in order to intend that the structure of the optical pick-up device is simplified, and the cost is reduced, also in the optical pick-up device having the compatibility, it is preferable that the optical parts for the high density optical disk and the optical parts for DVD or CD are commonly used with each other, and the number of optical parts structuring the optical pick-up device is decreased to the utmost, and it can be said that it is most preferable that the objective optical system is used in common with each other.
Further, following the recent price-reduction of the optical disk player, the cost reduction of the optical pick-up device is advanced. It conducts the effort to reduce the number of optical parts structuring the optical pick-up device to the utmost in each of manufacturers. In such a movement, as the optimum laser light source for the optical pick-up device having the compatibility for a plurality of kinds of optical disks in which the wavelength for the recording/reproducing is different from each other, a laser light source in which a light-emitting point which light-emits the laser light flux whose wavelength is different, is formed in one chip, is developing. Hereupon, in the present specification, a laser light source in which a plurality of light-emitting points whose oscillation wavelengths are different from each other, are housed in one casing, is referred to “packaged multiple light source unit”. It includes the light source unit in which a plurality of light-emitting points whose oscillation wavelengths are different from each other, are formed on one chip, and a light source unit in which a plurality of light sources whose oscillation wavelengths are different from each other, are housed in one casing.
An objective optical system which can be used in combination with the packaged multiple light source unit in which, in such a manner, the light-emitting points are provided closely, is disclosed in the following reference document (Patent Document 1). In this objective optical system, for the purpose that the laser light flux of wavelength 660 nm and the laser light flux of wavelength 785 nm, projected from closely provided light-emitting point, are converged onto the information recording surface of DVD and CD respectively, the magnifications of the objective optical system for respective wavelengths, are set to almost equal.
(Patent Document 1) Tokkai 2001-76367
However, a problem that, in the objective optical system having the compatibility for three kinds of optical disks of the high density optical disk, DVD and CD, when the magnifications of the objective optical system to respective wavelengths are set to almost equal, because the degree of freedom of the optical design which can be used for the improvement of optical characteristic, is taken, in a process of the optical design of the objective optical system, good optical performances for respective wavelengths can not be obtained, is actualized.